Method of annealing aluminum



United States Patent Ofiee 3,459,605 Patented Aug. 5, 1969 ABSTRACT OF THE DISCLOSURE Reduction in staining of aluminum by rolling oil is obtained by adding 002 to 2 weight percent of an organotin compound to the oil. Less than 0.5 weight percent gives as good a result as can be obtained with more of the additive. The oil is one normally used in metal rolling, i.e., viscosity 35-75 SUS at 100 F. An example is an oil having a viscosity of 56 SUS at 100 F. and containing 0.0625 Weight percent dibutyltin dilaurate. Diisopropyltin dilaurate also gives very good results. The annealing can be conducted at lower temperatures than before because of the reduced staining.

This invention relates to the processing or fabrication of aluminum. More particularly, it concerns the prevention of staining of aluminum during the operation of annealing the metal. In particular the invention relates to the annealing operation conducted with a film of hydrocarbon lubricant on the surface of the aluminum wherein the hydrocarbon contains a small amount of an organotin compound.

In fabricating aluminum into the form of plates or sheets, the met-a1 is conventionally subjected to a rolling operation wherein it is passed one or more times through a rolling mill to press it into the desired form. In this operation lubricating oil customarily is applied continuously to the rollers to reduce friction and minimize the energy expenditure. Usually the oil used for this purpose is of relatively low viscosity, for example, within the range of 35-300 SUS at 100 F., although oils of higher viscosity are used in some cases. Most of the commercial aluminum rolling operations are carried out by utilizing a petroleum oil having a viscosity between 35 and 75 SUS at 100 F. The aluminum plates or sheets which leave the rolling mill retain on their surface a thin film of the oil which has been applied as lubricant.

During the rolling operation the aluminum tends to undergo What is referred to as work hardening; and it is customary thereafter to anneal the hardened aluminum by subjecting it to a temperature above 600 F. Work hardened aluminum will anneal satisfactorily at a temperture of, for example, 650 F., and it is desirable to conduct the annealing step at about this temperature level. However, it has been found that at such temperature staining of the aluminum will occur due to the presence of the surface film of hydrocarbon oil, and that the surface generally will be left in a discolored, unsightly condition. This is apparently due to formation from the oil of a thin varnish-like deposit which adheres strongly to the metal and which cannot be removed by wiping. Hence, in order to avoid such staining in commercial practice, the aluminum is customarily annealed at a temperature sufiiciently high to burn off the varnish deposit, usually 800-850 F. The use of such higher temperature substantially increases the expense of the annealing operation.

The present invention is directed to the avoidance of the above-described stain formation during annealing of the aluminum. According to the invention, lubrication during the rolling operation is effected by means of a hydrocarbon oil in which has been incorporated a minor amount of an organo-tin compound having the structure wherein R R R and R are selected from the group consisting of hydrocarbon radicals, hydrocarbonoxy radicals and carboxylic acid radicals and R is selected from the group consisting of hydrocarbondioxy radical and a dicarboxylic acid radical. Preferably R R R and R are selected from the group consisting of alkyl, cycloalkyl, alkaryl, aralkyl, aryl, OR and wherein R is alkyl, cycloalkyl, alkaryl, aralkyl or aryl further characterized in that R R R R and R have 1 to 20 carbon atoms and R is a radical having 2 to 10 carbon atoms selected from the group consisting of and wherein R is aliphatic, alicyclic or aromatic.

Hence, the oil film which remains on the aluminum when it is subjected to the annealing step contains a minor proportion of such organo-tin compound. It has been found that at relatively low annealing temperatures, the presence of the organo-tin compound substantially reduces the amount of surface stain.

Practice of the invention thus involves lubrication of the roller surfaces with hydrocarbon oil containing a. minor amount of organo-tin compound containing oil to a suitable annealing temperature sufiicient to remove the oil film and leave the aluminum surface in an unstained condition. Suitable annealing temperatures for practicing the invention generally lie within the range of 600800 F. and are less than are normally required in conventional practice.

The base oil to which the organo tin is added may be any of the usual hydrocarbon oils used as rolling lubricant. It usually will be preferable to employ an oil of viscosity within the range of 35-75 SUS at F., although oils having viscosities as high as, or higher than 300 may be used if desired.

Only a small amount of organo tin compound need be incorporated in the base oil to secure the desired antistraining effect. The amount should be in excess of 0.02 weight percent based on organo-tin oil mixture but not in excess of 2.0 weight percent. Generally less than 0.5 weight percent of the organo-tin compound can be used. It has been found, surprisingly, that there is, in fact, no real advantage to use more than about 0.5 weight percent of the organo-tin compound and concentration of less than 0.5 weight percent provides at least as good stain prevention and in some cases better stain prevention than higher concentrations.

Any suitable procedure maybe used for incorporating the organo-tin compound in the base oil. Generally the desired quantity of organo-tin compound is added to the oil and the mixture is heated slightly, for example, to 120 to 130 F. to facilitate dissolution and is agitated until all of the organo-tin compound has dissolved in the oil. No further treatment is required, and the composition may be used immediately for practicing the invention or may be stored for future use.

The hydrocarbon substituted radicals on the stain reducing compounds of the invention are normal, branched chain or cyclic hydrocarbon radicals. Aliphatic, alicyclic or aromatic radicals are suitable. It is preferred that the aliphatic and alicyclic substituent radicals are saturated although inhibitors with unsaturated aliphatic and alicyclic substituent radicals can be used. Preferred hydrocarbon radicals are those having about 1 to 20 carbon atoms per radical. Examples of specific hydrocarbon radicals which are suitable substituents on the stain inhibitors of this invention are methyl, ethyl, propyl, butyl, amyl, cyclohexyl, dodecyl, lbutenyl, cyclohexenyl, cyclopentyl, isobutyl, isopropyl, benzyl, phenyl, tolyl, xylyl, cumyl, cymyl, pseudocymyl, naphthyl, anthryl, phenanthryl and the like.

The organo-tin inhibitors hydrocarbonoxy substituent radicals are any of the above-described hydrocarbon radicals connected by an oxygen atom to the tin atom of the organo-tin compound. Preferred molecular size of the hydrocarbonoxy radical substitutents is about 1 to 20 carbon atoms. Specific examples of suitable substituent hydrocarbonoxy radicals are methoxy, ethoxy, propoxy, isopropoxy, butoxy, cyclopentoxy, cyclohexoxy, benzyloxy, phenoxy, toloxy and the like.

The carboxylic acid substituents on the stain inhibitors of the invention are any of the above-described hydrocarbon radicals connected by to the tin atom of the inhibitor. Preferred molecular size of the carboxylic acid substituents is about 2-21 carbon atoms. Specific examples of suitable carboxylic acid substituent radicals are acetic, propionic, butyric, lauric, stearic, naphthenic, benzoic, hexahydrobenzoic, isobutyric, o-toluic acid, -toluic acid, isovaleric, 3-butenoic, senecioic acid radicals and the like.

The staining inhibitors used in the invention can be dicarboxylic acid substituted compounds or hydrocarbondioxy substituted compounds. The dicarboxylic acid or hydrocarbondioxy substituent radicals are illustrated by R in the above structural formula. The dicarboxylic acid substituent comprises a hydrocarbon connected by two groups to the metal atom of the organo-tin compound. The hydrocarbondioxy substituent comprises a hydrocarbon connected by two oxygen atoms to the metal atom of the organo-tin compound. The hydrocarbon portion of the hydrocarbondioxy and dicarboxylic acid substituents can be aromatic or it can be saturated or unsaturated aliphatic or alicyclic. It is preferred that the hydrocarbon portion of the dicarboxylic acid and hydrocarbondioxy substituents have a molecular size of about 2 to carbon atoms. Specific examples of suitable hydrocarbondioxy substituent radicals are ethylenedioxy, 1,2-propy1- enedioxy, 1,3-propylenedioxy, 1,2-butylenedioxy, 1,3- butylenedioxy, 1,4-butylenedioxy, 1,4-dioxy, Z-butene, 1,2-dioxy benzene, 1,3-cyclohexylenedioxy radicals and the like. Specific examples of suitable dicarboxylic acid radicals are maleic, 1,2-benzenedicarboxylic, muconic,

TABLE I Oil A B C 1 Viscosity, SUS at F 56 59. 4 API gravity at 60 F. 24. 3 22. 2 25. 7 Flash; open up deg. F., min 280 350 205 Pour point deg. F., max 50 45 -50 Conradson carbon, percent max Nil Trace Trace 1 Oil 0 is Oil A after solvent extraction and acid treatment.

Oils containing the tin compounds covered by this invention were evaluated by the Alcoa Stain Test 471 (4-61). In this test, 0.8 ml. of oil is spread on the surface of a standard test plate. This plate is then placed in an electric mufile which has been preheated to 650i5 F. for at least one hour before running the test. After 30 minutes, the plate is withdrawn and the stain compared with standards made with Alcoa Standard Stain Oils 1, 2, 3, 4 and 5. The intensity of staining increases with increasing numbers. A #1 rating indicates no stain; a #5 rating is a multicolored red and green (peacock) stain on a brown background. A plus indicates the appearance of the sample was somewhat better than the standard and a minus indicates the appearance was somewhat below the standard, but in either case, the difference Was not sufficient to change the rating.

The results of the test are set forth in Table II.

TABLE II Concentra- Additive tion Stain rating Oil A:

Diisopropyltin dilaurate 0 3 Diisopropyltin dilaurate 0.125 1 Dibutyltin dilaurate. 0. 5 2- Dibutyltin dilaurate 0.25 1+ Dibutyltin dilaurate 0. 1+ Dlbutyltin dilanrate 0. 0625 l-l- Dibutyltin di-2-ethylhexoate 0. 5 3 Dibutyltin di-2-ethylhexoate. 0. 25 3 'lriphenyltin stearate 0. 5 3 Triphenyltin acetate 0. 5 1 2 Tribut-yltin acetate 0. 5 2+ Oil B:

Dibutyltin dilaurate. 0 5 Dibutyltin dllaurate. 0. 5 5 Dibutyltin dilaurate 0. 25 2 Dibutyltin dilaurate 0. 125 2 Dibutyltin dilaurate 0. 0625 2 Oil 0:

Diisopropyltin dilaurate 0 3 Diisopropyltin dilaurate 1. 0 2 Diisopropyltin dllaurate- 0. 5 l Dtisopropyltin dilaurate 0. 25 1+ Dibutyltin dtlaurate. 0. 5 3+ Dibutyltin dllauratm. 0. 25 1+ 1 Test on filtered solution because additive not soluble; concentration unknown.

The invention claimed is:

1. In the annealing of aluminum having a surface film of hydrocarbon lubricant thereon, the method of preventing staining of the aluminum which comprises subjecting the aluminum to an annealing temperature in the presence of a surface film of lubricant comprising hydrocarbon oil having incorporated therein a minor amount of an organo-tin compound having a structural formula selected from the group consisting of wherein R R R and R are selected from the group consisting of alkyl, cycloalkyl, alkaryl, aralkyl, aryl, -OR and wherein R is alkyl, cycloalkyl, alkaryl, aralkyl or aryl further characterized in that R R R R and R have 1 to 20 carbon atoms and R is a radical having 2 to carbon atoms selected from the group consisting of wherein R is aliphatic, alicyclic or aromatic.

-2. The method according to claim 1 wherein the amount of organo-tin compound is in the range of 0.02 to 2.0 weight percent.

3. The method according to claim 2 wherein the amount of organo-tin compound is less than 0.5 weight percent.

4. The method according to claim 1 wherein the annealing temperature is in the range of 600 to 800 F.

References Cited UNITED STATES PATENTS 2,151,285 3/1939 Toussaint 148-131 2,829,076 4/1958 Rue 14820.6 2,861,020 11/1958 Mills 148-20.6

L. DEWAYNE RUTLEDGE, Primary Examiner G. K. WHITE, Assistant Examiner US. Cl. X.R. 

